Modulating system



E. PETERSON MODULATING SYSTEM Flled Aprll 15 1925 March 30 1926.

ll H Q 0% M" fl L w. M

Ma? y lnwmar: [a me Pefersm Patented Mar. 30, 1926.

UNITED STATES nucnnn rn'rnnson, or raw Yonx, n. Y., assren'on, BY mnsnn nssmnnnnrs, 'ro

1,578,679 PATENT OFFICE.

WESTERN ELEUIBIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

MODULATING SYSTEM.

Application fled April 15, 1925. Serial No. 23,282.

To all whom it may concern:

Be it known that I, EUGENE Pn'rnnson, a citizen of the United States of America, residin at New York, in the county of New York, tate of New York, have invented certain new and useful Improvements in Modulating Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to modulating systems and more particularly to tandem arrangements of modulating devices.

An object of the invention is to increase the modulated output of a space discharge modulating and amplifying system.

It is well known that space discharge am lifiers function simultaneously as ampl' ersand as modulators, due to the nonlinear relation that exists between the impressed E. M. F. and the space current. If the impressed E. M. F. is a. single pure sinusoidal wave the modulation products appear in the output as harmonics together with a steady D. 0. component, and if the impressed wave comprises two or more sinusoidal components'the modulation products will comprise a large number of components including those whose frequencies are the sum and the difference of the impressed wave frequencies.

In high frequency transmission systems, it is a common practice to modulate a carrier wave in accordance with a low frequency signal and subsequently to amplify the modulated carrier wave in one or more stages of amplification prior to transmiss1on.

In accordance with this invention, the subsequent stages of amplification are caused to contribute additional modulation products of the useful frequencies and in the proper phases so that the final modulated output is increased.

An object of the invention is therefore to provide a modulating and am lifying system in which the functions 0 modulatlon and amplification are usefully combined in a single device.

The nature of the invention and its mode of operation is more fully disclosed in the detalled description which follows read in conjunction with the accompanying drawing of which Figs. 1 and 2 represent in schematic form two systems embodying the invention in alternative forms.

The system of Fi 1 is arranged to deliver a speech modu ated carrier frequency current to a load impedance 6, which may in (practice be a wire transmission line, or a ra iatlng antenna system, or other type of load by which the energy is usefully absorbed, The carrier frequency wave is supplied by a high frequency generator 8 from WhlCh it passes through high-frequency transformer 9 to the input of space discharge device 1 and subsequently through similar space discharge devices 2 and 3. The s ace discharge devices 1, 2 and 3 are amp ifying vacuum tubes of the well known three-electrode type. They are coupled in tandem by means of high frequency transformers 4 and 5 and the last tube 3 is connected to the load by high frequency transformer 7. v

The speech waves by which the carrier wave is modulated are generated in microphone 10 and are transmitted through transformer 11 to the primary windings of the three low-frequency transformers 12, the secondary windings of which are connected in 'the input circuits of the successive ampllfier tubes 1, 2 and 3. Low pass filters 13 of similar construction are connected between each of the transformers 12 and the source of speech waves to prevent the feeding back of carrier frequency energy through the speech input circuits. These filters may be of the well known Campbell type as disclosed in U. S. Patent 1,227,113

issued May 22, 1917, but if the carrier wave frequency is very high, as it would be in some radio systems, it will in many instances be s'ufiicient to use, instead of the filters, simple condensers connected in shunt across the rimaries of transformers 12, or a single con enser across the secondary winding of transformer 11.

Space current is supplied to the discharge tubes from direct current sources 15 and the control electrodes are polarized by batteries 14. The voltages of thepolarizing batteries should be such that the discharge tubes operate under substantially similar conditions. It is preferable that the control electrodes be polarized negatively under whichv condition a positive increment of the control electrode potential will produce an increase in the space current greater than the decrease produced by an equal negative increment. In other Words the preferred condition of operation is that under which the space current increases more rapidly than the control electrode potential. If the discharge tubes are all alikethe potentials of batteries 14 should be equal but if tubes of frequency transformers ,9, 4 and 5 serve to make the system'substantially non-reactive to high frequency waves, and so to'prevent undesirable changes in phase of these waves as they are repeated by the successive discharge tubes.

' The manner in which the system operates and the precautions that must be taken to secure the desired object will now be described.

With respect to the carrier frequency wave the system operates simply as a multistage amplifier, the wave from source 8 being repeated with successively amplified energy by the discharge tubes 1, 2 and 3 and finally delivered to the load 6.

The speech waves impressed upon the control electrodes of each tube cause corresponding speech frequency currents toflow in the space paths, and these, interacting with the amplified carrier frequency currents, generate additional waves or modulation products, the important products being those of the summation and of the difference fre:

quencies, or, as they are commonly called,

In each tube therefore there are generated se arate side band waves, and further in tubes 2 and 8 the side band Waves generated in or repeated by the previous tubes are also present.

The successful operation of the system depends upon these various side band waves being substantially in phase in the output circuit of each tube so that they reinforceeach other. By similarly poling the windings of transformers a, 5 and 9 the phase of the carrier ware impressed on each tube may be made the same. It follows therefore that the side band products of tube 1 will, in' the output circuit of tubes 2 and 8, be in the same phase as in the output of. the first tube.

wraevo By poling alike the windings of transformers 12 also, the separately generated side bands will be of like phase in the output circuits of all tubes, and, since they are repeated by the successive tubes without change of phase, the desired result of their mutual reinforcement is obtained.

The system of Fig. 2 differs from'that of Fig. 1 in that the'carrier and speech wave sources are connected to the first tube only and are impressed u n the succeeding tube by being repeated tlii ough a coupling circuit designed to transmit efliciently waves of both high and low frequencies. The input circuit of space discharge tube 19 is connected to a, microphone circuit by transformer 17 and to the source 8 of carrier waves by transformer 18. The succeeding discharge tube 20 is connected to the output terminals of tube 19 by a coupling circuit comprising a high inductance choke coil 22 through which the space current for tube 19 is supplied, a series condenser 23 of high capacity, and a high resistance 24 connected in shunt to the input terminals of tube 20. The modulated wave output of tube 20 is delivered to the load'impedance 6 through high frequency transformer 25.

The operation of this system is similar to that of the system already described. With the direct coupled arrangement of the tubes the phase of the carrier wave is the same at the input terminals of each tube as also is the phase of the speech Wave. The separately generated side bands are therefore in like phase in the output circuit of each tube and consequently the side bands repeated by the second tube are in phase with those separately generated therein. The mutual reinforcement of the side band components is therefore obtained by this system also.

What is claimed is:

1. A modulating system comprising a plurality of space discharge amplifiers having anodes, cathodes, and control electrodes, coupling circuits for connecting said amplifiers in tandem whereby waves repeated in the space path of one amplifier are impressed upon the control electrode of the succeeding amplifier, a source of carrier waves, a source of signal waves, means for impressing simultaneously upon the control electrode of said amplifiers waves derived from both of said sources whereby the carrier wave is separately modulated in each amplifier, and means for controlling the phases of the waves in the space path of each amplifier so that the modulation products separately pro duced reinforce the modulation products, repeated from the preceding amplifiers.

2. A modulation system comprising a plurality of space discharge amplifiers having 'anodes, cathodes and control electrodes, a

source of carrier waves, and a source of signal waves, said amplifiers being connected in tandem to the source of carrier waves, and the control electrodes of each of said amplifiers being coupled separately to said source of signal waves.

3. A modulation system comprising a plurality of space discharge amplifiers having anodes, cathodes, and control electrodes, 2. source of carrier waves, said amplifiers being connected in tandem to said carrier wave source, a source of signal waves, and coupling means for impressing said signal waves upon the control electrode of each amplifier separately, said coupling means being adapted to control the phases of the impressed signal waves whereby the modulation products separately produced in each amplifier are caused to reinforce similar products repeated from the preceding amplifiers.

4. A modulation system comprising a plurality of space discharge amplifiers having anodes, cathodes and control electrodes, 21 source of carrier waves, said amplifiers being connected in tandem to said source by coupling circuits selective to carrier frequencies, a source of low frequency waves individual coupling circuits for impressin said low frequency waves upon the contro electrode of each amplifier, and means included in said coupling circuits to prevent the transfer of carrier frequency waves therethrough, said coupling circuits being adapted to control the phases of the impressed low frequency waves whereby the modulation products separately produced in each amplifier are caused to reinforce similar products repeated from the preceding amplifiers.

5. A modulation system comprising a plurality of space discharge amplifiers in tandem having anodes,

cathodes and control electrodes, the control electrodes of saidspect to the control electrode potentials, in-

put circuits and output circuits connected respectively between the control electrodes and the anodes to the cathodes of said amplifiers, a source of low frequency waves, a source of high frequency waves, transformers selective to high frequencies connected in said inputand said output circuits whereby the amplifiers are connected in tandem to said high frequency source, and transformers efiicient' at low frequencieshaving their secondarywindings connected in said input circuits and their primary windings con-' nected in common to said lowfrequency source, the windings of said high frequency transformers being similarly poled and the windings of said low frequency transformers being also similarly poled whereby the modulation products generated in each amplifier are caused to reinforce similar products repeated from the preceding amplifier.

6. A. modulation system comprising a plurality of space discharge amplifiers each having an anode, a cathode, and a control elect-rode, a circuit including said amplifiers connected in tandem, a source of carrier waves, a source of signal waves, means for supplylng waves from said sources to said amplifier circuit to produce modulation products in each amplifier and means for controlling said amplifiers so that the modulation products produced by each" amplifier reenforce the modulation products repeated thereby.

In witness whereof, I hereunto subscribe my name this 10th day of April, D. 1925,

EUGENE PETERSON. 

